A HYCOM modeling study of the Persian Gulf: 1. Model configurations and surface circulation

The circulation and water mass transformation processes in the Persian Gulf and the water exchange with the Indian Ocean through the Strait of Hormuz are studied using the Hybrid Coordinate Ocean Model (HYCOM). Model results show that the Indian Ocean Surface Water (IOSW) propagates in two branches into the gulf, one along the Iranian coast toward the northern gulf and the other one onto the southern banks driven by the Ekman drift due to the prevailing northwesterly winds. These two branches of inflow form two cyclonic gyres in the northern and in the southern gulf. A salinity front separates the fresher intruding IOSW from the saltier waters in the gulf. Eddies with size of about 100 km are fully developed along the salinity front in summer. The intrusion of the IOSW in the model extends much farther into the gulf in summer than in winter. By analyzing the salt balance in the basin and conducting sensitivity experiments, we show that it is the balance between the advection of IOSW and vertical salt flux induced by mixing that mainly controls the seasonal variation of the surface salinity. Surface wind stress plays a secondary role in modulating the seasonal intrusion of the IOSW. High-frequency atmospheric forcing produces more realistic surface temperatures than obtained from climatological forcing, as a result of increased heat loss in winter. However, the high-frequency forcing does not change significantly the general features of the circulation.